A standard nozzle for an injection-molding machine has an elongated body centered on an axis and formed with an axially and longitudinally throughgoing passage, a threaded rear end, an outer wall, and a front end. A removable nozzle element is fitted in the passage at the front end and an electrical heating element fits tightly on the outer wall. A protective sleeve coaxial with the body surrounds and encloses the body and heating element and has a front end at the body front end. An end ring is fitted in the front end of the gap between the sleeve and the body to close this space.
The problem with this arrangement is that the front end of the nozzle is subjected to considerable stress, in particular as the shot is made when molten plastic is forced under very high pressure from the nozzle. This pressurized mass exerts a considerable backward force on the end ring, often pushing it back into the space between the sleeve and the body. This not only compresses the heating element, but often lets plastic get into the space between the sleeve and the body where it can bulge out the sleeve. Since the nozzle normally fits with close tolerances in a passage in a mold, when it is thus bulged out it does not fit properly and can get jammed.